Two-spotted spider mite (TSSM), Tetranichus urticae Koch is a major pest wherever strawberry plants are grown in Sri Lanka. This pest was not controlled by the Department of Agriculture recommended synthetic insecticide Abamectin in many instances. Use of biological agents for the control of TSSM is globally a common practice and thus Phytoseiulus persimilis (Athias-Henriot) and Neoseiulus californicus (McGregor) were imported from Koppert biological systems, Netherlands. An experiment was conducted to investigate the possibility of using and N. californicus (McGregor) and P. persimilis (Athias-Henriot) in combination and N. californicus (McGregor) alone to control TSSM under laboratory conditions. The results indicated that the use of N. californicus alone was not effective in controlling the TSSM, though the TSSM population was maintained at low levels. However, the combination of biological agents was very effective by controlling the TSSM population with an 85% reduction. There was no population growth of biological agents after introduction and their population was reduced over the time. Further, there was a significant redcution in TSSM population after fifth week when the biocontrol agents were applied in combination. It was concluded that the application of P. persimilis and N. californicus was effective in controlling T. urticae rather than applying N. californicus alone. The biological control can be proposed as an alternative to insecticide, Abamectin.

Keywords: Abamectin, Biological control, Tetranichus urticae, Strawberry